Thymus grafts have been shown to produce tolerance to MHC and non-MHC antigens as well as to induce MHC-restricted self-recognition. It is planned to study the role of antigen presentation on thymic stroma and thymocyte populations in this phenomenon. Neonatally thymectomized mice will be given syngeneic thymus grafts, previously "seeded" with allogeneic MHC or non-MHC antigen bearing thymocytes. The effect of these grafts on tolerance and self-recognition will be examined. The role of thymic stroma in antigen presentation will be examined in similar fashion by "seeding" allogeneic thymic stroma or stroma bearing the non-MHC antigen with syngeneic thymocyte populations. The resulting tolerance in the above models will be examined in an effort to elucidate the mechanism(s) i.e., the presence of suppressor cell populations, humoral suppressor factors, or cellular deletion mechanisms.